Conventional butterfly valve structures include a valve housing having a fluid conduit and a valve seat, a seal member that is movable between an open position and a closed position in the fluid conduit, and a mechanism for rotating the seal member between the open and closed positions. Typically, the seal member is a plate that is parallel to the direction of fluid flow in the open position and is rotated perpendicular to the direction of fluid flow in the closed position. The seal member engages the valve seat and seals the fluid conduit in the closed position.
Butterfly valves are used in a wide variety of applications. Different applications may involve liquids, gases and vacuum. Some applications may require a long operating life, with frequent cycling between the open and closed positions, and low particulate generation. An example of such an application is in equipment for vacuum processing of semiconductor wafers. As semiconductor device geometries decrease in size and circuit densities increase, semiconductor wafers are increasingly sensitive to particulate contamination. Components within the vacuum envelope of the processing chamber, such as butterfly valves in vacuum lines, are potential sources of particulate contamination. Furthermore, the failure of a butterfly valve may require all or part of a semiconductor fabrication line to shut down, thereby adversely affecting throughput. Accordingly, long operating life and low particulate generation are important butterfly valve characteristics.
Movement of the seal member into and out of engagement with the valve seat is a potential source of particulate contamination and wear. To alleviate these problems, prior art butterfly valve designs have employed combinations of rotary movement and linear movement of the seal member. Butterfly valves which operate by rotating the seal member from an open position into alignment with a valve seat, followed by linear movement of the seal member into engagement with the valve seat, are disclosed in U.S. Pat. No. 4,817,916, issued Apr. 4, 1989 to Rawstron; U.S. Pat. No. 4,921,212, issued May 1, 1990 to deQuay; and U.S. Pat. No. 5,330,157, issued Jul. 19, 1994 to Dern et al. Each of the disclosed butterfly valves includes a cam arrangement. A shut-off valve which includes a shifter rod and sliding guide closure mechanism is disclosed in U.S. Pat. No. 4,634,094, issued Jan. 6, 1987 to Geiser. All of the known prior art butterfly valve configurations have had one or more disadvantages, including limited operating life and high particulate generation.